Re: Hash index todo list item - Mailing list pgsql-hackers

From Mark Mielke
Subject Re: Hash index todo list item
Date
Msg-id 46E06E58.1080708@mark.mielke.cc
Whole thread Raw
In response to Re: Hash index todo list item  (Michael Glaesemann <grzm@seespotcode.net>)
List pgsql-hackers
Michael Glaesemann wrote:
> On Sep 6, 2007, at 10:53 , Mark Mielke wrote:
>> I don't like the truncating hash suggestion because it limits the 
>> ability of a hash code to uniquely identify a key.
> AIUI, a hash can't be used as a unique identifier: it always needs to 
> be rechecked due to the chance of collisions. There might be other 
> issues with truncation, but preventing hashes from being unique isn't 
> one of them.

Of course - that's why I used the word "limit".

Hash works best, when the key is unique, however. A 32-bit hash will be 
many powers of 2 more unique than a 8-bit hash.

Cheers,
mark

-- 
Mark Mielke <mark@mielke.cc>


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